<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>后盾人</title>
    <style>
        * {
            padding: 0;
            margin: 0;
            box-sizing: border-box;
        }

        main {
            position: absolute;
            left: 50%;
            top: 50%;
            transform: translate(-50%, -50%);
        }

        ul {
            display: flex;
            list-style: none;
        }

        ul li {
            margin-right: 10px;
        }

        ul li strong {
            padding: 5px 30px;
            background: #27ae60;
            text-transform: uppercase;
            color: white;
            cursor: pointer;
        }

        ul li strong+div {
            position: relative;
            display: flex;
            flex-direction: column;
            background: #95a5a6;
            padding: 10px;
            transform: scale(0);
            transition: .6s;
            z-index: -1;
            transform-origin: left top;
        }

        ul li strong+div a {
            color: white;
            text-decoration: none;
            padding: 5px 0;
        }

        ul li:hover strong+div {
            transform: scale(1);
        }
    </style>
</head>

<body>
    <main>
        <ul>
            <li>
                <strong>video</strong>
                <div>
                    <a href="">HDCMS</a>
                    <a href="">PHP</a>
                </div>
            </li>
            <li>
                <strong>live</strong>
                <div>
                    <a href="">LINUX</a>
                    <a href="">CSS3</a>
                </div>
            </li>
        </ul>
    </main>
</body>

</html>